Project Summary/Abstract Osteonecrosis of the jaw (ONJ) is associated with antiresorptive therapy. The pathophysiology of ONJ is unknown and no established treatment is currently available. Although ONJ occurs in patients taking oral bisphosphonates, it predominantly develops in patients on intravenous bisphosphonate therapy for the treatment of bone metastatic diseases. These patients typically have a history of multiple chemotherapy and/or steroid therapy. Therefore, chemotherapeutics and/or steroids likely contribute to the development of ONJ. The objective of this project is to determine the effect of the combination of chemotherapeutics and antiresorptives on lymphangiogenesis and to delineate the impact of suppressed lymphangiogenesis in the pathogenesis of ONJ. The long-term goal is to elucidate the pathophysiology of ONJ to enhance risk assessment and to establish preventive and management protocols. We have shown that antiresorptive therapy impedes osseous wound repair of the jaw resulting in the retention of necrotic bone and suppresses genes related to lymphangiogenesis. We further found that lymphatic vessel formation was impaired in healing of tooth extraction sockets in animals given the combination of chemo- and antiresorptive-therapy. To further our findings and to clarify the pathophysiology of ONJ, this proposal will test the hypothesis that the combination of antiresorptives and chemotherapeutics hinders wound healing by suppressing lymphangiogenesis. The murine model of ONJ established in our laboratory will be utilized in this study. As the significance of lymphangiogenesis during tooth extraction socket healing has not yet been established, we will first determine the impact of impaired lymphangiogenesis on tooth extraction socket healing using physical and biochemical strategies. Next, the mechanisms of chemotherapy-suppressed lymphangiogenesis will be investigated with a focus on podoplanin, which is an essential molecule for lymphangiogenesis. Lastly, the function of podoplanin in tooth extraction socket wound healing will be determined by assessing the downstream signaling of the CLEC2 pathway. CLEC2 is a specific and only known receptor for podoplanin. This study will identify impaired lymphangiogenesis via the podoplanin/CLEC2 interaction as a key mechanism of the development of ONJ. This research is critical to establish preventive and treatment protocols for ONJ.